Add support for booting from cciss devices

Those controllers create links in the form:

/dev/disk/by-path:
pci-0000:0b:08.0-cciss-disk0 -> ../../cciss/c0d0
/dev/disk/by-id:
cciss-3600508b1001035393520202020200005 -> ../../cciss/c0d0
Merge pull request #157 from dirkmueller/pebbles-cciss

Add support for booting from cciss devices